Electronic components mounted on Printed Circuit Boards (“PCBs”) are pervasive throughout a wide range of consumer and industrial products. With recent advances in semiconductor technologies, these electronic components have become smaller, faster, and more powerful. They have also become more densely packed in the PCBs, which may include many layers of intricate electrical circuits and connections supporting the components. This miniaturization has led to several new challenges in electronic component and PCB design, including the ability to control the heat generated by the electronic components during their operation.
A considerable amount of heat may be generated by electronic components during their operation, including transistors, integrated circuits, power controls, switches, oscillators, microprocessors, and the like. The heat generated may cause component failure or malfunction if not properly controlled. Certain types of electronic components may be particularly susceptible to heat dissipation or other temperature effects. In some cases, the temperature must be stabilized for the components to remain within their operating range.
For example, voltage-controlled crystal oscillators (“VCXOs”) or oven-controlled crystal oscillators (“OCXOs”), are highly sensitive to temperature gradients, both in time and across their physical dimensions. These temperature gradients may result in undesirable output fluctuations such as thermally induced frequency drift. These output fluctuations may in turn impact the quality of real-time applications and services in computer networks where these oscillators are heavily used, including Pseudo-Wire Emulation (“PWE”), Voice over IP (“VoIP”), video conferencing, and streaming services.
Conventional approaches to control or stabilize the temperature in a PCB include the use of heat sinks and temperature compensation circuits mounted on or external to the PCB, as well as thermally-insulated enclosures to house the PCB. For example, heat sinks are typically mounted on the active surface of a semiconductor die to absorb heat from the die and dissipate the heat by convection into the cooler air, thereby maintaining the temperature across the PCB.
Additional temperature control may be provided by temperature compensation circuits which generally stabilize the performance of a given electronic component or PCB across a wide range of temperatures. In the case of VCXOs and OCXOs, temperature compensation circuits may provide a relatively flat frequency output over a wide range or temperatures.
The PCB and temperature compensation circuits may be enclosed within a thermally-insulated enclosure or housing to protect the PCB and electronic components therein from outside environment hazards, such as ambient heat, moisture, dust, debris, and so on. Thermally-insulated housings may also be used to prevent electromagnetic signals generated by the electronic components from causing Electromagnetic Interference (“EMI”) or Radio Frequency Interference (“RFI”) to other devices in their vicinity and vice-versa.
The thermally-insulated housings may also include temperature sensors to monitor the temperature around electronic components within the housings. In cases where temperature stability is desired for optimal performance, one or more heating elements may be used together with the sensors to maintain a given temperature gradient across a component. Based on the temperature measured by the sensors, the heating elements may generate more or less heat to achieve the desired temperature gradient.
For example, a single planar heating element has been used to thermally stabilize electronic components mounted on a PCB within a thermally-insulated housing. Though a single planar heating element may stabilize time-based thermal fluctuations for a given electronic component, it may not compensate for thermal gradients across the physical dimensions of the component. These thermal gradients are dependent on the relative positions of other heat-generating electronic components on the PCB, such as power supplies.
A set of linear heating elements that are closely spaced and in parallel may also be used. Although a set of linear heating elements may provide some capability to vary the heating across the physical dimensions of the component, the set may be insufficient to eliminate output fluctuations that degrade real-time applications and services, such as in the case of VCXOs and OCXOs that must maintain a flat frequency output over a wide range of temperatures.
Accordingly, it would be desirable to provide a thermal-management approach that can effectively stabilize temperature gradients across an electronic component mounted on a PCB across both time and the physical dimensions of the component.